For more information, contact: Vegetable Crops Research Program Department of Plant Sciences, University of Saskatchewan http://www.usask.ca/agriculture/plantsci/vegetable/ Vegetable Program Department of Plant Sciences, College of Agriculture and Bioresources Lettuce has excellent potential as a year-round indoor crop. Lettuce grows rapidly, even in situations of relatively low light and temperatures. Buttercrunch (aka Boston bibb or semi-head lettuce) type lettuce is particularly well-suited to indoor production as it produces compact high quality plants that can be harvested one leaf at a time or as an entire mature head. Recirculating hydroponic systems allow very effective use of growing space and nutrients and are well suited to indoor production of high value crops such as lettuce. The University of Saskatchewan, working with the Greenhouse Growers Association of Saskatch- ewan has been conducting research into the best methods of growing buttercrunch lettuce in simple hydroponic production systems. Production in hydroponic systems started with 4 week old lettuce seedlings grown in rockwool cubes (2.5 cm * 2.5 cm * 3.0 cm deep). The seedlings were grown at room temperature at moderate light levels and were fertilized weekly with 20-20-20 plus micronutrients at 100 ppm N. After 4 weeks the lettuce seedlings were about 10 cm tall and had 6 true leaves (Fig. 1) – at which point they were large enough to be trans- planting into the hydroponic production system. The University of Saskatchewan has evaluated the performance of 26 different cultivars of buttercrunch type lettuce in hydroponic production. So far, the best cultivars have been ... Growing Hydroponic Lettuce www.usask.ca/agriculture/plantsci/vegetable/ Figure 1. Four week old lettuce seedlings grown in rockwool being moved to the hydroponic system • Red Sails (Johnny’s Seeds) - produced excellent yields of large, red/green open-type heads. Red Sails received the highest flavor rating of all cultivars tested. • Optima (Osborne Seeds) - is a great looking and good tasting semi-head type lettuce • Lettuce was ready to harvest 4-6 weeks after being trans- planted into the hydroponic system – with the rate of growth and size of plants harvested being highly dependent on cultivar grown and the amount of light provided to the crop. No problems with disease or insect pests have been observed. Algae tend to build up in the systems as each crop progressed. A thorough clean up of the entire production system at the end of each crop cycle was important for controlling algae and also prevented disease problems. Clean up involves flushing out the system to remove any root material, scrubbing off any algae, then rinsing with a dilute (5%) solution of bleach, followed by a final rinse with clean water. Seedling production -Seed of a suitable variety -Rockwool plugs or Jiffy pots to grow transplants Floating Culture system -Sheet of 2 cm thick Styrofoam -Nutrient Holding Tank – should be at least 30 cm deep and hold 1 L of nutrient solution for each lettuce plant being grown -Aquarium aeration pump + air stone NFT (Nutrient Film Technique) System -Grow troughs – standard rectangular or circular eaves troughs work well although the materials used have not been made to Food Grade Standards -Submersible water pump (10 L/min capacity is plenty) -2 cm diam PVC tube to carry nutrient solution from the reservoir to high end of the NFT system -100 mesh in-line filter – removes plant debris from the circulating nutrient solution -1 cm diam spaghetti tubing - to take the nutrient solution from the PVC supply hose to each production trough -0.5 to 1L/min pressure compensated emitters – regulate the rate of flow of nutrient solution into each trough -Nutrient holding tank – see description in floating culture system -Aquarium aeration pump and air stone Crop Growth Figure 4. Research technician Chris Fazekas harvesting mature butter- crunch lettuce from a NFT hydroponic system. Floating culture tanks are in the background. Note the algae build up in the catch trays used to collect the nutrient solution flowing through the NFT troughs. Parts List
Transcript
For more information, contact:
Vegetable Crops Research Program Department of Plant Sciences, University of Saskatchewan http://www.usask.ca/agriculture/plantsci/vegetable/
Vegetable ProgramDepartment of Plant Sciences, College of Agriculture and Bioresources
Lettuce has excellent potential as a year-round indoor crop. Lettuce grows rapidly, even in situations of relatively low light and temperatures. Buttercrunch (aka Boston bibb or semi-head lettuce) type lettuce is particularly well-suited to indoor production as it produces compact high quality plants that can be harvested one leaf at a time or as an entire mature head.
Recirculating hydroponic systems allow very effective use of growing space and nutrients and are well suited to indoor production of high value crops such as lettuce.
The University of Saskatchewan, working with the Greenhouse Growers Association of Saskatch-ewan has been conducting research into the best methods of growing buttercrunch lettuce in simple hydroponic production systems.
Production in hydroponic systems started with 4 week old lettuce seedlings grown in rockwool cubes (2.5 cm * 2.5 cm * 3.0 cm deep). The seedlings were grown at room temperature at moderate light levels and were fertilized weekly with 20-20-20 plus micronutrients at 100 ppm N. After 4 weeks the lettuce seedlings were about 10 cm tall and had 6 true leaves (Fig. 1) – at which point they were large enough to be trans-planting into the hydroponic production system.
The University of Saskatchewan has evaluated the performance of 26 different cultivars of buttercrunch type lettuce in hydroponic production. So far, the best cultivars have been ...
Growing Hydroponic Lettuce
www.usask.ca/agriculture/plantsci/vegetable/
Figure 1. Four week old lettuce seedlings grown in rockwool being moved to the hydroponic system
• Red Sails (Johnny’s Seeds) - produced excellent yields of large, red/green open-type heads. Red Sails received the highest flavor rating of all cultivars tested.
• Optima (Osborne Seeds) - is a great looking and good tasting semi-head type lettuce
• Lettuce was ready to harvest 4-6 weeks after being trans-planted into the hydroponic system – with the rate of growth and size of plants harvested being highly dependent on cultivar grown and the amount of light provided to the crop. No problems with disease or insect pests have been observed. Algae tend to build up in the systems as each crop progressed. A thorough clean up of the entire production system at the end of each crop cycle was important for controlling algae and also prevented disease problems. Clean up involves flushing out the system to remove any root material, scrubbing off any algae, then rinsing with a dilute (5%) solution of bleach, followed by a final rinse with clean water.
Seedling production
-Seed of a suitable variety
-Rockwool plugs or Jiffy pots to grow transplants
Floating Culture system
-Sheet of 2 cm thick Styrofoam
-Nutrient Holding Tank – should be at least 30 cm deep and hold 1 L of nutrient solution for each lettuce plant being grown -Aquarium aeration pump + air stone
NFT (Nutrient Film Technique) System
-Grow troughs – standard rectangular or circular eaves troughs work well although the materials used have not been made to Food Grade Standards
-Submersible water pump (10 L/min capacity is plenty)
-2 cm diam PVC tube to carry nutrient solution from the reservoir to high end of the NFT system
-100 mesh in-line filter – removes plant debris from the circulating nutrient solution
-1 cm diam spaghetti tubing - to take the nutrient solution from the PVC supply hose to each production trough
-0.5 to 1L/min pressure compensated emitters – regulate the rate of flow of nutrient solution into each trough
-Nutrient holding tank – see description in floating culture system
-Aquarium aeration pump and air stone
Crop Growth
Figure 4. Research technician Chris Fazekas harvesting mature butter-crunch lettuce from a NFT hydroponic system. Floating culture tanks are in the background. Note the algae build up in the catch trays used to collect the nutrient solution flowing through the NFT troughs.
Parts List
Lettuce grows well in either Floating Culture or Nutrient Film
• Floating culture - Is the simplest production system. Plants are grown on a cm thick sheet Styrofoam that floats on top of a nutrient solution held in a grow tank (aquarium, plastic tub etc)(see Fig. 2). The 4 week old lettuce seedlings are inserted into holes cut through the Styrofoam block so that the roots are fully immersed in the nutrient solution, but the growing point remains above the nutrient solution. The nutrient solution is kept aerated using a standard aquarium aeration system. Spacing plants about 20 cm apart allows enough space for the lettuce to reach full size without wasting space.
• Nutrient film technique (NFT) - in NFT production, plants are grown in troughs and a thin film of nutrient solution is kept circulating down the troughs and past the root system. The production troughs can be as simple as sections of circular or rectangular eaves trough (Fig. 3). Trough lengths are kept relatively short (<5m) to minimize nutrient and oxygen gradients. A hole saw is used to cut holes (5cm diameter) into the upper surface of each trough. The holes are large enough to allow the 4 week old lettuce transplants in their rockwool plugs to be dropped easily to the bottom of the trough – with the leaves arranged so that they protruded through the hole in the top of the trough. The holes were spaced 20cm apart and the troughs were also spaced 20 cm apart – this spacing provided each plant with enough room to reach full size, without wasting space. The troughs were kept on a 2% slope so that the nutrient solution ran down the trough and over the root systems. At the end of each trough the nutrient solution was gathered back into a capture tank and then pumped back to the top of the channels using a small circulating pump. The nutrient solution was pumped through the production troughs at the rate of 1L/min. Insufficient flow volumes result in depletion of nutrients and oxygen as the nutrient solution runs down each channel. However, excessive high flow rates waste pumping capacity and may interfere with uptake of certain nutrients. The 1L/min flow rate was achieved by installing pressure compensated button-type emitters in the spaghetti tubes that supplied each grow channel. These emitters are available locally from suppliers of irrigation equipment. However, these emitters are easily plugged by plant debris or algae in the nutrient solution. Installing a 100 mesh in-line filter just upstream of the emitters solved this plugging problem. Four troughs operating at 1L/min could be run off a single circulating pump. The nutrient solution in the capture tank was kept aerated using a small aquarium pump.
Figure 2. Floating culture hydroponic system showing lettuce plants floating on Styrofoam blocks with the root system immersed in aerated nutrient solution
• Successful hydroponic production depends on supplying the plants with an adequate, well-balanced nutrient supply. Nutrient recommenda-tions for hydroponic lettuce are presented in Table 1. While it is possible to purchase pre-mixed complete nutrient formulations suited for general hydroponic production, creating your own nutrient solution will allow you to more closely meet the needs of your selected crop and in the long run will also be more cost effective.
• Hydrobuddy is a powerful, yet easy to use program designed to assist growers in preparing nutrient solutions for hydroponic crop production. Hydrobuddy is available as a free download and can be located by entering “Hydrobuddy” in your favorite search engine.
Crop and Nutrient Management
Figure 3. NFT Hydroponic System. A thin film of nutrient solution runs over the root system as the nutrient solution flows down the slightly sloped production trough. At the end of the trough the nutrient solution is captured in a holding tank where it is aerated prior to being pumped back to the top of the trough.
• Hydroponic lettuce grows best at pH of 6.0, whereas the water in Saskatoon has a pH of around 8.0. Adding household white vinegar to the nutrient solution at the rate of 2-3 mL/L gave the required shift in pH. The amount of nutrient solution to prepare depends on the size of your nutrient holding tank and the number and size of plants being grown. About 1L of solution per plant is more than enough to meet the nutrient and water requirements of lettuce from transplanting through to maturity.
Table 1. Recommended fertility regime for hydroponic lettuce (from Hydrobuddy).
